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An unusually rich and diverse suite of virgianid brachiopods, hitherto poorly known, is systematically described here for the first time from the Ordovician–Silurian boundary interval (late Katian – Aeronian) of North Greenland. The Late Ordovician virgianids comprise typical taxa of the warm‐water Tcherskidium fauna (e.g. Tcherskidium tenuicostatum, Proconchidium schleyi, Holorhynchus giganteus and Deloprosopus dawesi sp. nov.). Among the early Silurian taxa, Virgiana hursti sp. nov. occurs as abundant shell beds, similar to other congeneric species in Laurentia, but has somewhat larger internal skeletal structures, albeit not as extravagantly developed as in the late Katian virgianids; Borealoides balderi gen. et sp. nov. shows extreme thickening of the shell wall and internal structures, approaching the extravagant calcification of Katian virgianids. The highly distinctive mid‐Aeronian stricklandioid brachiopod genus, Kulumbella, characterized by a shell with criss‐cross (divaricate) ribbing, also occurs in North Greenland, represented by K. heimdali sp. nov., which has the largest and most strongly biconvex shells for the genus. Palaeogeographically, the Late Ordovician virgianid fauna of Laurentia was highly distinct, confined to the low–mid tropical latitudes north of the palaeoequator. In comparison, the early Silurian (Rhuddanian) Virgiana and some related taxa in Laurentia spanned the tropics of both hemispheres, forming extensive shell beds in carbonate basins, although Borealis and Borealoides gen. nov. remained confined largely to the northern hemisphere, suggesting a certain level of provincialism extending into the earliest Silurian. A palaeoecological preference for warm‐water carbonate settings would explain the unusual abundance and richness of the virgianid faunas in North Greenland. [ABSTRACT FROM AUTHOR]

The Late Ordovician (late Katian) Tcherskidium fauna consisted of large- and thick-shelled virgianid pentamerid brachiopods characterized by large and ribbed shells of Tcherskidium and Proconchidium and usually associated with Holorhynchus, Deloprosopus, and Eoconchidium. This unique fauna was widely distributed across several tectonic plates, largely confined to the paleoequatorial and especially the northern paleotropical zones, such as northern Laurentia, accretionary terranes of Alaska, Kolyma, Baltica, Siberia, Kazakh and adjacent terranes, and South China. In Laurentia, the eponymous genus Tcherskidium was predominant in regions north of the paleoequator and, in sharp contrast, was absent south of the paleoequator. In this study, Tcherskidium lonei n. sp. and Proconchidium schleyi n. sp. are described from Alaska and North Greenland, respectively, adding new data on the Tcherskidium fauna of the Late Ordovician Northern Hemisphere. Shell gigantism, together with the sharp paleobiogeographic division, suggests that the Late Ordovician (late Katian) Northern Hemisphere had a prevailing warm-water mass, probably due to the lack of large landmass beyond the northern tropics. This was in sharp contrast to the Southern Hemisphere, which was frequently influenced by cold-water invasions from the ice-bearing Gondwana supercontinent centered on the South Pole. UUID: http://www.zoobank.org/25d9b772-bd7d-4ad6-bfc6-ba02b1567cf3 [ABSTRACT FROM AUTHOR]

A Late Ordovician brachiopod fauna from the Black River quadrangle (D-1 1:63,360 scale) of east-central Alaska comprises taxa typical of the Late Ordovician brachiopod fauna in the pericratonic epeiric seas of Laurentia, including Hesperorthis pyramidalis (Twenhofel, 1928), Plaesiomys occidentalis (Okulitch, 1943), Eoplectodonta sp., Holtehdalina sp., Leptaena sp., Brevilamnulella minuta n. sp., Tcherskidium tenuicostatum n. sp., Rhynchotrema iowense Wang, 1949, and Whitfieldella sp. The presence of Plaesiomys occidentalis and Tcherskidium tenuicostata n. sp. indicates a latest Katian age by correlation with similar species in the Mackenzie Mountains, southern Manitoba, Anticosti Island, the American midcontinent, Kolyma, and Siberia. Cluster analysis based on 20 well-studied late Katian brachiopod faunas from various regions within Laurentia and elsewhere in other tectonic plates suggests that the small brachiopod faunule from Alaska has the strongest paleobiogeographic affinity with Laurentia, confirming that the Black River quadrangle of Alaska was part of Laurentia during the Late Ordovician. UUID: http://zoobank.org/6b387856-61d5-4685-a592-faf5287c1e0f [ABSTRACT FROM AUTHOR]

Dalmanelloid brachiopod shells were collected from the Upper Ordovician Lexington Formation (lower Katian) of Kentucky, Sheguindah Shale (middle Katian) on Manitoulin Island, Ontario, and the Stony Mountain Formation (upper Katian) in the Winnipeg area, Manitoba. They were investigated to test the hypothesis of paleo-latitudinal zonation of the shelly benthos. A multi-technique approach was applied to evaluate the petrographic and geochemical (isotopic and elemental) preservation of the secondary layer of shells. Preliminary conventional microscopy, cathodoluminescence (CL), and scanning electron microscopy (SEM) confirmed the retention of primary shell ultrastructure (prismatic low-Mg calcite). The geochemical diagenesis proxies (e.g., Sr, Mn, Fe, and ΣREE) show insignificant correlations with the δ18O and δ13C values, thus supporting the preservation of at least near-primary geochemical compositions. Among the three lots of shells, the mean δ18O value is the highest in those from the Lexington Formation (–4.5‰ ± 0.3‰ VPDB), lowest from the Stony Mountain Formation (–6.8‰ ± 0.4‰ VPDB), and intermediate from the Sheguindah Shale (–6.0‰ ± 0.8‰ VPDB). The relative gradient in δ18O increase is in agreement with the paleo-latitudinal gradient, with Kentucky in subtropical, southern Ontario in mid-tropical, and southern Manitoba in subequatorial latitudes. The Lexington Formation shells also have the highest mean δ13C value (0.8‰ ± 0.2‰ VPDB) and relatively high P contents (170 ± 27 ppm), suggesting higher organic productivity, which is consistent with previous interpretation of frequent upwelling of nutrient-rich cool waters along the southeastern margin of Laurentia during the Katian. The Lexington shells also have a lower mean Th/U (0.6 ± 0.6), which is consistent with blooming organic productivity that likely led to more consumption of oxygen in the water column. [ABSTRACT FROM AUTHOR]

Pentameroides is a large-shelled pentameride brachiopod, which was widespread throughout Laurentia in the early Silurian (Telychian). Evolving from Pentamerus in the early Telychian, it dispersed from its subtropical - high tropical origin to subequatorial intracratonic seas by the late Llandovery. In this study, large collections of reef-dwelling Pentameroides septentrionalis from the Attawapiskat Formation, Akimiski Island, Nunavut, and level-bottom-inhabiting Pentameroides subrectus from the Fossil Hill Formation, Manitoulin Island, Ontario, and the Jupiter Formation, Anticosti Island, Quebec, were biometrically analyzed for seven external morphological features. Bivariate and ordination analysis (principal components analysis) revealed that P. septentrionalis has a more globose, more biconvex shell with a larger ventral umbo than P. subrectus. These morphological differences, coupled with their excellent preservation in shallow-water reefal environments, suggest that P. septentrionalis was adapted to a relatively low-turbulence, hurricane-free, nutrient-stressed environment near the equator (<10°S) while P. subrectus lived in storm-dominated higher tropical latitudes (∼15°S-25°S). This interpretation is corroborated by the morphology of level-bottom-dwelling Harpidium and Sulcipentamerus from the paleoequatorial lower Silurian of North Greenland, which exhibit morphological features similar to those of P. septentrionalis, even though they did not inhabit a reefal environment. Principal components analysis reveals that P. septentrionalis resembles P. subrectus in early ontogeny, suggesting that P. septentrionalis evolved from P. subrectus as it moved northwards from high tropical to near-equatorial settings. [ABSTRACT FROM AUTHOR]

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The palaeocontinent Laurentia experienced pulses of major marine transgression during the Late Ordovician (Katian) and was covered by extensive equatorial to subtropical epicontinental seas. Brachiopods that evolved in the newly created habitats showed increasingly strong endemism from the early to late Katian. At the faunal level, the Laurentian epicontinental brachiopod (LEB) fauna became ubiquitous in the epicontinental seas, with a high level of generic homogeneity but little in common with the coeval faunas in other palaeotropically located tectonic plates. At the level of species distribution, there was limited mixing between palaeoequatorial intracratonic basins and higher tropical to subtropical pericratonic shelves within Laurentia by late Katian. This was demonstrated by the palaeogeographical distribution of several species lineages and morphological clines along latitudinal and other ecological gradients. Such a high level of endemism suggests an extreme specialization of the LEB fauna in the tropical epicontinental seas, which made it most vulnerable to the drastic climate change and mass extinction during the Hirnantian glaciation. [ABSTRACT FROM AUTHOR]

Multivariate analysis of 197 well-preserved specimens among 11 species of late Late Ordovician (Katian and Hirnantian) plaesiomyid brachiopods from North America revealed two trends of morphological changes: (1) increasing globosity and dorsal convexity from the early to late Katian, and (2) coarser, but fewer ribs in species from the paleoequatorial intracratonic seas compared with species from the mid- to high-tropical pericratonic shelves and platforms. Another notable change, albeit not quantified, was the enlargement of cardinal process in plaesiomyids from early to late Katian, characterized by a predominantly trilobed cardinal process in the intracratonic species versus a bilobed cardinal process in pericratonic species. Increases in dorsal convexity and shell globosity are interpreted to have allowed for development of a larger lophophore, improving the capacity and efficiency of filter feeding and gas exchange. Smaller but more frequently bifurcating ribs would have led to more numerous setae near the margin of the shell, resulting in increased sensitivity to environmental stimuli. Increased size and number of lobes of the cardinal process would have allowed for larger diductor muscles to open a larger, heavier shell. In this study, two new species, Plaesiomys periosa sp. nov. and Plaesiomys lenzi sp. nov., are proposed, and two existing species are transferred from Dinorthis to Plaesiomys. [ABSTRACT FROM AUTHOR]

Multivariate analysis based on nine biometric characters of 171 Late Ordovician rhynchonellide specimens from nine upper Sandbian-upper Katian localities in North America supports the hypothesis that one of the diagnostic taxa of the North American epicontinental brachiopod fauna, Hiscobeccus, evolved from Rhynchotrema, which lived predominantly in peri-cratonic settings. The oldest known Hiscobeccus, H. mackenziensis of early Katian age, exhibits transitional characteristics between Rhynchotrema and Hiscobeccus, and it clusters more closely with Rhynchotrema than with younger species of Hiscobeccus of mid-late Katian (Maysvillian-Richmondian) age. Diversification of the Hiscobeccus lineage in epicontinental seas was characterized by drastic increase in shell size, globosity and lamellosity, especially in palaeoequatorially located inland basins. Such morphological trends are interpreted as adaptation to relatively shallow, muddy substrates, moderate water turbulence, relatively low oxygen content and unstable supply of nutrients in generally overheated epicontinental seas with sluggish circulation. [ABSTRACT FROM AUTHOR]

Abstract: Massive-bedded Thalassinoides ichnofacies occurs pervasively in widely separated areas on the vast Upper Ordovician carbonate platforms along the palaeoequator of Laurentia, from the Børglum River Formation in North Greenland, through the Red River Formation and Bighorn Dolomite of the Williston Basin (Manitoba, Canada to Wyoming, USA), to the Ely Springs Dolomite and equivalent strata of the eastern Great Basin (Utah and Nevada, USA). The Late Ordovician Thalassinoides is characterised by complex, three-dimensional, anastomosing or multi-level galleries that are consistent in size, pattern and density, with preserved depth of 1m or greater. In addition to the similar Thalassinoides burrows, the ichnofacies across the palaeocontinent also contains typical taxa of the Red River biota, such as the soccer-ball sized receptaculitid Fisherites, large-shelled, diverse and abundant nautiloids, the distinctively planispiral gastropod Maclurina, as well as diverse tabulate and rugose corals. The consistent characteristics of the Red River biofacies and Thalassinoides ichnofacies suggest a palaeogeographically homogeneous and temporally stable depositional environment along the palaeoequatorial belt of Laurentia during the pre-Hirnatian Late Ordovician. The Thalassinoides ichnofacies marked the first phase of mega-scale invasion of burrowers into relatively deep-water platform and shelf environments by successively creating a well-oxygenated deep burrow system for protection and deposit feeding. Such substrate tiering expansion constituted an important aspect of the Great Ordovician Biodiversification Event. [Copyright &y& Elsevier]

The most common forms of Late Ordovician dalmanellid brachiopods from the Cincinnatian type area, previously treated as either Dalmanella or Onniella, are assigned to Cincinnetina gen. nov. The new genus differs from Dalmanella and Onniella in having a consistently developed primary medial costa in the dorsal valve, a larger cardinal process that tends to develop a trilobed myophore, strongly differentiated fine and coarse punctae, and sparse aditicules. Cincinnetina can be distinguished from the closely related Paucicrura and Diceromyonia in its smaller trilobed cardinal process (when developed) that does not have a dominant medial lobe and does not extend into the delthyrial cavity of the ventral valve. Globally, Dalmanella and Onniella occur most commonly in deposits of relatively deep- or cool-water palaeoecological settings, whereas in North America, Cincinnetina, Paucicrura and Diceromyonia are found mainly in carbonate-rich deposits in warm-water depositional environments, with Cincinnetina and Paucicrura most common in pericratonic settings and Diceromyonia in palaeoequatorial inland seas. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)